• Paint has an extremely simple user interface strictly following the desktop metaphor. Because of this, there is no way a user can go wrong with Paint. There is one window, one canvas and one toolbar/ribbon area to deal with. There is the pallet area too (prior Windows 7); but most users are OK with it.
• Paint starts fast: you don’t have to wait a few minutes to use Paint. It has such a small memory footprint and will start before you are done doing with double-click. Another benefit of the small memory footprint is that you don’t need a fancy computer to run Paint on.
• You can only use the most common file types with Paint. Here again, you do something, and save the file in your format of choice without being presented a handful of post-save options. The file is just saved and ready to be used in a few clicks.
• You will never rip apart the Paint UI by accident. Most modern software are designed with ‘total UI flexibility’ in mind so that there are 101 toolbars and menus to a density where people are scared to move the mouse pointer across the screen with the fear of moving one part of the UI and sticking it in another area rendering a total mess in the GUI. Paint doesn’t have this pervasive silliness.
• Paint is ubiquitous. Buy a new computer and Paint will be pre-installed with it; go to a friend’s PC and Paint could be found there; it’s installed by default on every PC since Windows 95. It’s totally available to you during the lifetime of your computer and will never expire asking you for a new serial number.

Certainly these aren’t the only reasons why someone would like Paint. For most people, the main reason to like Paint is its simplicity and availability. A normal user doesn’t fancy sophistication in software. They want their job done, in the easiest way and in the shortest time. Maybe there are the same reasons why Notepad is the most famous text editor for Windows.